Motor inhibition and cognitive flexibility in pathologic skin picking ☆ Brian L. Odlaug a , Samuel R. Chamberlain b , Jon E. Grant a, ⁎ a Department of Psychiatry, University of Minnesota, 2450 Riverside Avenue, Minneapolis, MN, 55454, United States b Department of Psychiatry, University of Cambridge, Box 189, Level E4, Addenbrooke's Hospital, Hills Road, Cambridge CB2 2QQ, United Kingdom abstract article info Article history: Received 6 October 2009 Received in revised form 26 October 2009 Accepted 6 November 2009 Available online 13 November 2009 Keywords: Cognition Impulse control Pathological skin picking Trichotillomania Background: Individuals with pathologic skin picking (PSP) often report significant difficulty resisting the urges and drive to engage in picking behavior. Studies have shown significant inhibitory deficiencies (i.e. increased impulsivity) in subjects with other putative obsessive–compulsive spectrum disorders, such as trichotillomania, using objective tests. This study sought to assess motor inhibitory control and aspects of cognitive flexibility in a sample of individuals with PSP. Method: Twenty subjects with PSP (mean age 33.1 ± 14.3 years; 85% female) and 20 healthy controls (mean age 31.6 ± 9.1 years; 85% female) underwent cognitive assessments using the Stop-signal and Intra- dimensional/Extra-dimensional (ID/ED) set-shift tasks. Groups were matched for age, gender, and education. Results: PSP was associated with significantly impaired stop-signal reaction times but intact ID/ED cognitive flexibility compared to controls. Measures of disease severity in the PSP subjects did not covary significantly with stop-signal performance. Conclusion: The finding of impaired inhibitory control but intact set-shift cognitive flexibility draws remarkable parallels with findings in trichotillomania but differs from obsessive compulsive disorder. These findings have important implications for understanding potential neurobiological dysfunction in PSP, how the disorder should be classified, and suggest new potential treatment directions. © 2009 Elsevier Inc. All rights reserved. 1. Introduction Pathologic skin picking (PSP) is characterized by repetitive and compulsive picking of skin which causes tissue damage. Although there have been no population-wide epidemiological studies of PSP, it has an estimated prevalence rates of 2.0%–5.4% in the general population (Keuthen et al., 2000; Hayes et al., 2009). Individuals with PSP report that picking behavior causes scarring and infections, impairment in daily functioning, and significant distress stemming from their inability to control the behavior (Gupta et al., 1986; Arnold et al., 1998; Odlaug and Grant, 2008a,b). The compulsive and repetitive behaviors seen in PSP and other grooming behaviors such as trichotillomania (TTM) have led to the hypothesis that they be classified as disorders of the obsessive– compulsive spectrum (Stein and Hollander, 1995). The often overwhelming urges to pick or pull coupled with a sense of relief or calm after engaging in the behavior reported by those with PSP and TTM are very similar to the urges to engage in compulsive acts reported by those with obsessive compulsive disorder (OCD). Studies have also shown significant clinical similarities between PSP and TTM such as age of onset, gender ratio, psychosocial functioning, and clinical severity (Cohen et al., 1995; Odlaug and Grant, 2008a). Furthermore, the body-focused, repetitive nature of PSP shares similarities to the compulsive acts seen in disorders such as OCD (Stein et al., 2006, 2008). Due to these phenomenological connections, tests of neurocognitive functioning have been examined in tricho- tillomania and OCD (Rettew et al., 1991; Keuthen et al., 1996; Coetzer and Stein, 1999; Bohne et al., 2005; Chamberlain et al., 2006). Chamberlain et al. (2006) measured motor inhibition (impulsivity) and aspects of cognitive flexibility in a group of 17 trichotillomania subjects, 20 OCD subjects, and 20 healthy controls (Chamberlain et al., 2006). Significant deficits of motor inhibition (Stop-signal task) were noted in both the trichotillomania and OCD groups but only the OCD group showed deficits in extra-dimensional set-shifting (assessed using the CANTAB intra-dimensional/extra-dimensional, ID/ED set- shift task). While set-shifting appears to be intact in trichotillomania, other aspects of cognitive flexibility may be impaired in this disorder. Bohne et al. (2005) reported impaired performance in trichotilloma- nia subjects on the Object Alternation Test, while Stanley et al. (1997) showed impaired performance on Trails B test. Despite the above research into other putative OC spectrum conditions, there have—to the knowledge of the authors—been no Progress in Neuro-Psychopharmacology & Biological Psychiatry 34 (2010) 208–211 Abbreviations: ADHD, Attention Deficit Hyperactivity Disorder; CGI, clinical global impression; HARS, Hamilton Anxiety Rating Scale; HC, healthy control; HDRS, Hamilton Depression Rating Scale; IDED, intra-dimensional extra-dimensional; OCD, obsessive compulsive disorder; PSP, pathological skin picking; SCID, Structured Clinical Interview for DSM-IV; SP-SAS, Skin Picking Symptom Assessment Scale; SP-YBOCS, Yale Brown Obsessive Compulsive Scale Modified for Skin Picking; SSRT, stop-signal reaction times; TTM, trichotillomania. ☆ All work completed in Minneapolis, Minnesota, United States. ⁎ Corresponding author. Tel.: + 1 612 273 9736; fax: + 1 612 273 9779. E-mail address: grant045@umn.edu (J.E. Grant). 0278-5846/$ – see front matter © 2009 Elsevier Inc. All rights reserved. doi:10.1016/j.pnpbp.2009.11.008 Contents lists available at ScienceDirect Progress in Neuro-Psychopharmacology & Biological Psychiatry journal homepage: www.elsevier.com/locate/pnp